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Antioxidant Activity of Flavonoid

In vitro study

The reactivity of an antioxidant is determined by its reactivity as a hydrogen or electron-donating agent, the fate of the resulting radical (unpaired electron), its reactivity with other antioxidant, and its metal-chelating potential. The reactivity can be assessed by applying the chromogenic redox indicator ABTS+(radical cation of 2,2'-azino-bis (3-ethylbenzthiazoline 6-sulphonic acid) relative to Trolox (water-soluble vitamin E analogue).

The strength of antioxidant activities is ordered as:

  • the ortho 3',4'-dihydoroxy moiety in the B-ring,
  • the meta 5,7-dihydroxy moiety in the A-ring, and
  • the 2,3-double bond together with both 4-keto and 3/5-hydroxy group in the C-ring.
Glycosylation decreases the activity. Metal chelation is achieved by the first and the third items above.

For example, quercetin is a more effective photoprotectant and anti-oxidant than kaempferol. [1] [2]

  1. Ryan KG, Swinny EE, Markham KR, Winefield C (2002) "Flavonoid gene expression and UV photoprotection in transgenic and mutant Penunia leaves" Phytochem 59:23-32 PMID 11754940
  2. Li J, Ou-Lee T-M, Raba R, Amundson RG, Last RL (1993) "Arabidopsis flavonoid mutants are hypersensitive to UV-B irradiation" Plant Cell 5: 171-179 PMID 12271060

In vivo study

Although antioxidant activities of flavonoids are several times higher than vitamin C or E in vitro, their plasma and intracellular concentration after intake is over 100 times lower than vitamin C or uric acid. The antioxidant function in vivo is therefore considered negligible[1].

Plasma concentration of major antioxidants
vitamin C 40-60 μmol/L

Vitamin C level predicts strokes. [2]

uric acid 200-300 μmol/L

Urate, vitamin C and E account for the total antioxidant activity. [3]

vitamin E 8-28 μmol/L

Mean plasma tocopherol from 36 different studies.[4]

flavonoids < 10 μmol/L for flavanones
< 1 μmol/L for anthocyanins
  1. Lotito SB, Frei B (2006) "Consumption of flavonoid-rich foods and increased plasma antioxidant capacity in humans: cause, consequence, or epiphenomenon?" Free Radic Biol Med 41(12):1727-1746 PMID 17157175
  2. Myint PK, Luben RN, Welch AA, Bingham SA, Wareham NJ, Khaw KT (2008) "Plasma vitamin C concentrations predict risk of incident stroke over 10 y in 20649 participants of the European Prospective Investigation into Cancer–Norfolk prospective population study" Am J Clin Nutr 87(1)64-69 PMID 18175738
  3. Maxwell SR, Thomason H, Sandler D, Leguen C, Baxter MA, Thorpe GH, Jones AF, Barnett AH (1997) "Antioxidant status in patients with uncomplicated insulin-dependent and non-insulin-dependent diabetes mellitus" Eur J Clin Invest 27(6):484-490 PMID 9229228
  4. Farrell PM (1980) Vitamin E: a comprehensive treaties (Machlin LJ ed.) pp.520-620, Marcel Dekker, New York

Table for antioxidant activities

Relative total antioxidant activities[1]
Antioxidant Sources Activity* (mM)
Vitamins
Vitamin C fruit and vegetables 1.0 ± 0.02
Vitamin E grains, nuts and oils 1.0 ± 0.03
Anthocyanins
Oenin black grapes/red wine 1.8 ± 0.02
Cyanidin grapes, raspberries and strawberries 4.4 ± 0.12
Delphinidin aubergine skin 4.4 ± 0.11
Flavonols
Quercetin onion, apple skin, berries, black grapes, tea and broccoli 4.7 ± 0.10
Kaempferol endive, leek, broccoli, grapefruit and tea 1.3 ± 0.08
Flavones
Rutin onion, apple skin, berries, black grapes, tea and broccoli 2.4 ± 0.12
Luteolin lemon, olive, celery and red pepper 2.1 ± 0.05
Chrysin fruit skin 1.4 ± 0.07
Apigenin celery and parsley 1.5 ± 0.08
Flavan 3-ols
(Epi)catechin black grapes/red wine 2.4 ± 0.02
Epigallocatechin teas 3.8 ± 0.06
Epigallocatechin gallate teas 4.8 ± 0.06
Epicatechin gallate teas 4.9 ± 0.02
Flavanones
Taxifolin citrus fruit 1.9 ± 0.03
Naringenin 7-rutinoside citrus fruit 0.8 ± 0.5
Naringenin citrus fruit 1.5 ± 0.05
Hesperetin 7-rutinoside orange juice 1.0 ± 0.03
Hesperetin orange juice 1.4 ± 0.08
Teaflavins
Teaflavin black tea 2.9 ± 0.08
Teaflavin 3-gallate black tea 4.7 ± 0.16
Teaflavin 3'-gallate black tea 4.8 ± 0.19
Teaflavin digallate black tea 6.2 ± 0.43
Hydroxycinnamates
Caffic acid white grapes, olive, cabbage and asparagus 1.3 ± 0.01
Chlorogenic acid apple, pear, cherry, tomato and peach 1.3 ± 0.02
Ferulic acid grains, tomato, cabbage and asparagus 1.9 ± 0.02
p-Coumaric acid white grapes, tomato, cabbage and asparagus 2.2 ± 0.06
* ... Measured as the Trolox equivalent antioxidant activity (TEAC) - the concentration of Trolox with the equivalent antioxidant activity of a 1 mM concentration of the experimental substance
  1. Rice-Evans C, Miller N, Paganga G (1997) "Antioxidant properties of phenolic compounds" Trends Plant Sci 2(4):152-159
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